High-resolution P-T-t paths from δ18O zoning in titanite: A snapshot of late-orogenic collapse in the Grenville of New York

Abstract

We characterize oxygen isotope zoning within single titanite crystals from the Carthage-Colton mylonite zone (CCMZ), Adirondack Mountains (New York State, United States), by ion microprobe. Smooth gradients of δ 18 O, up to 0.6‰ over 90 µm, resulted from diffusive exchange of oxygen during cooling from peak metamorphic temperatures of 650-700 °C. Modeling of the observed profi le indicates punctuated cooling rates of 30-60 °C/m.y. along the CCMZ, set within long periods of much slower cooling. These results indicate a previously unrecognized period of rapid cooling along the CCMZ that is interpreted to result from the post-Ottawan collapse of the Grenville mountain belt and exhumation of the central Adirondack Highlands at ca

Combined oxygen-isotope and U-Pb zoning studies of titanite: New criteria for age preservation

“…It appears that the S 2 and S 3 fabrics formed in rapid succession over a period ≤10 my, and possibly ≤5 my. Oxygen isotope zoning in T2 grains shows that at least the S 2 shear zones formed concurrently with rapid cooling brought on by tectonic exhumation of the Adirondack Highlands from beneath the Lowlands along the CCMZ (Bonamici et al, 2011(Bonamici et al, , 2014. Thus, the S 2 and S 3 fabrics are the structural record at Harrisville of late-Ottawan gravitational collapse (Fig.…”

“…Experimental data thus appear to successfully predict the relative diffusivities of O and Pb in natural hydrothermal samples that experienced cooling rates of~30-70°C/m.y. (Bonamici et al, 2011(Bonamici et al, , 2014. The lower blocking temperature of O indicates that δ 18 O zoning can be a useful tool for identifying preserved U-Pb age domains within high-temperature titanites.…”

“…Titanite grains for this study were sampled from two outcrops within the Carthage-Colton Mylonite Zone (CCMZ) near Harrisville, New York ( Fig. 2; Cartwright et al, 1993;Lamb, 1993;Bonamici et al, 2011Bonamici et al, , 2014. The CCMZ is a major NNE-striking structure that juxtaposes the upper-amphibolite-facies Adirondack Lowlands to the northwest and the granulite-facies central Adirondack Highlands to the southeast ( Fig.…”

Megacrystic Gore Mountain–type garnets in the Adirondack Highlands: Age, origin, and tectonic implications

“…The latest displacement along the Carthage-Colton shear zone has been shown to be top down to the northwest ca. 1047 Ma (Selleck et al, 2005), and to have proceeded very rapidly (Bonamici et al, 2011). The Lowlands are part of Rivers (2008) collapsed "orogenic lid" (i.e., orogen suprastructure) and exhibit only minor, low-grade Ottawan metamorphism, whereas the Highlands belong to the high-grade infrastructure of the large, hot allochthonous polycyclic belt that forms the hinterland of the Ottawan orogen (Fig.…”

Significance of “stretched” mineral inclusions for reconstructing P–T exhumation history

“…3). Owing Darling 2013) to slow cooling rates inferred for the Adirondack highlands, temperatures remained above 600 °C for 50-100 million years (Mezger et al 1991;Bonamici et al 2011). If P-T conditions during metamorphism at the Hooper Mine were based on cristobalite inclusions in garnet, one would interpret the garnets to have formed at T > 1470 °C and P < ~0.5 GPa, resulting in an error in inferred formation conditions of ~0.7 GPa and >600 °C and well outside the stability field of the host garnet.…”